Technicians often use the schematic to improve the brightness switch, modify the distortion character, or fix common noise issues in older units.
High and low gain inputs use standard resistor attenuators.
Transitioned to highly stable BBD chips and standardized op-amps. Added toggle switches for chorus selection. MN3007 BBD chip, MN3101 clock.
The heart of the JC-120 schematic is the analog modulation circuit. It is famous for using , specifically the historic MN3007 and its companion MN3101 clock driver. jc-120 schematic
Two independent input channels (Normal and Effect). Speakers: Dual 30cm (12-inch) "silver cone" drivers.
A secondary preamp featuring the distortion, reverb, vibrato, and chorus circuits.
The JC-120 schematic is structurally unique because it is designed from the ground up as a . Technicians often use the schematic to improve the
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Some pics that display cosmetic differences of JC-120's of different pedigrees: From top to bottom. - Very old version of the amp: Solid State Guitar Amp Forum jazz chorus jc-120 - Roland
Identical to Channel 1 but routes directly into the onboard Distortion, Reverb, Vibrato, and Stereo Chorus matrices. jazz chorus jc-120 - Roland Added toggle switches for chorus selection
For technicians, the JC-120 schematic reveals common failure points:
The pitch-modulated delay signal is sent exclusively to the Right power amplifier. Because the left speaker pumps out pure dry signal and the right speaker pumps out modulated wet signal, the "chorus" effect actually blends acoustically in the air, creating a massive, three-dimensional stereo image. 5. Dual Power Amplifiers
The schematic shows the signal being split before the BBD, ensuring one amp receives the raw, unaffected signal while the other receives the modulated signal. C. Power Amplifier Stage The power section is designed for massive headroom.
Following the gain stages, the signal enters the Equalization (EQ) section. The schematic reveals a Baxandall-style tone control circuit (or a variation thereof).
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